The present invention relates to improvements in the technique for mass transport operation and physical separation involving barriers. More particularly the invention relates to improvements in the technique for carrying out the transport of one or more components from a liquid or solid phase to another liquid or solid phase.
In our previous U.S. Pat. No. 4,454,231 a method and device have been disclosed for carrying out mass transfer operation and phases separation in the same piece of equipment, the device being referred to as "LIDEX" (Liquid Extraction Separation Device). The method comprises the introduction of the two liquids to be contacted into the mixing-reservoir, mixing the liquids and thus performing the mass transfer of the desired components from one phase to another. After allowing the formation of the interphase between said two liquids, the mixer-separator is pushed in until it reaches the interface, the liquid upper phase being forced through the bore of a sealing element located at the bottom of the mixer-separator and through a channel which traverses the vertical axis of the mixer-separator being accumulated into a container above the mixer-separator element. The method was found to be most efficient for a number of uses involving mass transfer and phase separation with liquids only and particularly for the immunoassay technique being extremely wide, versatile and competing very favourably with other known methods.
The method described in said previous patent was invented as a result of the efforts invested in order to find an efficient method to be applied in conjunction with our basic patent application on the use of liquid-liquid extraction technique for specific binding assay (Canadian Pat. No. 1,140,463). The method was found to be most suitable for any immunoassay technique such as radioimmunoassay, enzyme immunoassay, free radical assay or metalloimmunoassay (as described in U.S. Pat. No. 4,205,952). The use of the novel device according to the previous U.S. Pat. No. 4,454,231 provided a very simple and efficient method for the extraction procedure and following the separation of the liquid phase in the upper container of the device, it was possible to determine directly in the liquid phase by appropriate analytical methods any minute concentration of chemical substances.
One basic characteristic of the method and device disclosed in the previous U.S. Pat. No. 4,454,231, is the existence of a continuous region in the form of a channel, free of any obstruction, connecting the orifice bore at the base of the sealing element, with the container located at the upper end of the mixer-separator. Thus when the mixer-separator is pushed into the mixing reservoir, the forced liquid will flow up smoothly, without encountering any hindrance.
Today there is a large number of examples showing the successful applicability of the method described in our previous patent application in various fields involving mass transfer and physical separation between two liquid phases. The phase "mass transfer" refers to the motion of molecules or fluid elements caused by some form of potential or driving force and it includes molecular diffusion, transport by convection and simple mixing. Mass transfer is involved wherever a chemical reaction takes place. The reacting substances must come together if the reaction is to proceed. In the case of a reversible reaction, the concentration of reactants and products at any instant can be controlled if one or more reaction components are removed by mass transfer to a second phase in which no reaction takes place. Of particular importance to the problem in hand is transfer between two phases across an interface since this phenomenon is involved in most separation processes. Any method of contacting two phases which results in the selective interphase transport of one of the constituents can form the basis of a separation process. The selectivity can be the result of different equilibrium relations for the different species or it may be due to different rates of transport of the several constituents. Of particular interest for the present invention is the problem of mass transfer between a fluid and suspended particles and more particularly mass transport through selective barriers to achieve separation between the fluid and suspended particles, once the mass transfer effect has produced the desired degree of the physico-chemical and/or immunological reactions.
The prior art also describes a number of separation methods in immunoassay procedures for the bound and free fractions based on solid phase adsorption, various solids being suggested as adsorbants (e.g., charcoal, resin, silica, florisil etc.) of free antigens or precipitation agents for the bound phase, all of which end up with a system of suspended particles in a liquid medium. The selection of any particular technique is determined by consideration of many interrelated factors such as solubility of compound, characteristics of antiserum, fraction to be counted, degree of non-specific binding, and type of radioisotope. However one feature which is common to all the above methods is the need for a centrifugation step to effect aggregation of the suspended solid particles followed by a decantation or suction step, to physically separate the solid and liquid phases. Another main disadvantage of these methods is the fact that no full separation can be obtained between the bound antigen-antibody complex and the free unbound antigen. A recent elegant method in the solid phase adsorption of antibody is adsorption of antibodies to plastic tubes. Accordingly, a number of coated tubes are prepared in advance. The preparation and storage of large numbers of such tubes is a serious drawback in addition to the fact that these tubes are sensitive to variations in serum protein content.
To the best of our knowledge there is no prior art on the method of mass transfer and physical separation of the phases, both operations being carried out in the same device in accordance with the present invention.
In principle, the device according to the previous patent application could be conceived to be also useful concerning mass transport operation, from one phase to another, even when two different phases e.g. liquid-solid are utilized. However in this case some difficulties would be expected in the physical separation of the phases, since the liquid phase aspirated through the channel will also induce the entrainment of some solid phase particles.
Based on the principle of an ampoule having a hollow piston as disclosed in the U.S. Pat. No. 2,524,362, a test tube filter device having a hollow plunger with a porous bottom portion as filter, is described in the U.S. Pat. No. 3,512,940. A specific application using the principle of said device, has been later on described for separation of blood fractions in a number of U.S. Patents and German patent applications. A typical illustration of one of these publications are the German patent application Nos. 2,415,618 and 2,454,918 (or their corresponding U.S. Pat. No. 4,021,352 and U.K. Pat. No. 1,508,844).
The device described in these patents is specifically related to an apparatus for separating blood fractions. A piston with a hollow riser tube has at its bottom end a filter section which is permeable for the top layer fraction only. The piston is inserted into the cylindrical vessel and pushed downwardly, but only to the point where it is slightly above the interface of the heavier fraction. Special care has to be used in operating this device to avoid mixing of the two phases during the downward movement of the piston into the cylindrical vessel. The device has at its top a stopper which can be either open or closed.
Another device, to be used for blood separation, is described in the U.S. Pat. No. 3,969,250. According to the device disclosed therein, a plunger is movable into an outer tubular member closed at the lower end. A piston head having a downwardly extending inlet tube is attached to the lower end of the plunger. On the inlet tube is mounted an elastic membrane and below this barrier is positioned a slidingly removable piston rubber seal. During use, the rubber piston seal is separated from the surface of the serum, by an air column in order to avoid falling down of any blood cell, debris or solids wiped from the inner wall of the blood tube by the rubber piston seal, as the piston is forced downwardly.
The above devices are specifically for a qualitative determination, to be useful for processing blood serum specimens and separating the fractions thereof.
In principle, the device according to our previous U.S. Pat. No. 4,454,231 could be conceived to be also useful concerning mass transport operation from one phase to another, even when two different phases e.g. liquid-solid are utilized. However in this case some difficulties would be encountered in the physical separation of the phases, since the liquid phase aspirated through the channel will also induce the entrainment of some solid phase particles.